A. Technical Field
The present invention relates generally to signal analysis, and more particularly, to the application of one or more compliance transfer functions to a real-time signal.
B. Background of the Invention
A communication system comprises a transmitter, a channel or a medium for transferring a signal, and a receiver. The signal-transferring medium may be a metallic cable or fiber, free space in a wireless system or a backplane printed circuit board (“PCB”). The operation of these various communication systems, and components therein, may function according to specifications that may be defined by protocols, standards, etc. For example, the performance and operation of a transmitter may be defined to deliver a “zero-link” signal that meets certain specification parameters. Furthermore, other protocol specifications may define signal quality characteristics not at the output of a transmitter, but rather at a receiver.
The characteristics of a signal at a receiver may depend on the performance of the transmitter and the communications medium on which the signal is communicated to the receiver. In an attempt to develop a standard for interoperability comities, protocols and standards define specifications related to the signal quality at the receiver, as opposed to the specifying the transmitters characteristic. In order for this to be an effective standard or protocol, the characteristics of the communications medium or the load should be specified. During the transmission of the signal from the transmitter to the receiver, the signal characteristics may change as it travels on the communications medium. This change in signal characteristics may be measured or modeled, with varying effectiveness, by testing the transmission of the signal on a particular medium or modeling the transmission of the signal using simulation applications, such as Spice™.
Methods of analyzing the characteristics of a signal may be explained with reference to FIG. 1. The device or transmitter 101 to be analyzed transmits an electrical signal 104 onto a communications medium to a receiver. These signals 104 may be simulated by simulation applications 102, such as Spice™, or may be analyzed by physically transmitting the electrical signal on a communications medium 103, such as sample cables, attenuators or backplane.
In the first method, a Spice simulator 102 is used to make a spice model of the device 101. The simulator 102 attempts to model the transmission of an electrical signal on a communications medium. However, the simulator 102 oftentimes is unable to completely model and completely account for changes to a signal as it is generated and transmitted from a transmitter to a receiver device.
A Spice model generally considers the ideal conditions and environment of the device or system whereas the real model may have some type of error producing factors, which need to be considered as well. These error-producing factors may lie in the channel such as a co-axial cable that might have some variations in its construction caused by different manufacturing processes by different vendors. Further, the dielectric materials in insulators that are put in between different co-axial Cables may also vary. Further yet, backplane variations may be present across different vendor backplanes. Accordingly, a spice modulator is oftentimes unable to account for these different variations between vendor communications mediums and not accurately simulate a signal at a receiver within a particular system.
In the second method of analyzing an electrical signal, various cables, attenuators, sample backplanes or other physical communications mediums are built 103. These sample communications medium may be used by engineers in building the match cables, or a suitable load. The engineers may require the use of a network analyzer to extract S parameters from a cable or backplane. Various problems exist with this second method including additional cost associated with the construction and maintenance of physical communications mediums, and the network analyzer. Additionally, there may be mismatches between a test load and a communications medium that is actually employed within a system.
The inability to accurately test a load, including the corresponding communications medium, often gives rise to disagreements between a supplier and customer regarding the protocol specification compliance of a component within a particular system. Thus, in an attempt to develop a standard for interoperability comities it is essential to specify and accurately test the signal quality at a receiver prior to insertion within a system.